III-Nitride materials have been extensively studied and implemented in advanced solid state lighting technologies in recent decades. The III-Nitride platform has also attracted tremendous efforts in developing high performance active region for optoelectronic devices including detectors and solar energy convertors. Specifically, the demand for integrating devices covering a broad spectral regime in a single nitride-based material platform drives the further pursuit of III-Nitride materials with a tunable band gap property.
The identification of the narrow bandgap in InN binary alloys (˜0.64 eV) and large bandgap in AlN binary alloys (˜6 eV) has enabled access to broad energy gap coverage by utilizing corresponding ternary and quaternary alloys with different Indium (In)/Gallium (Ga)/Aluminum (Al) composition. For example, varying the Indium (In) composition in InGaN ternary alloy from very low to high In-content provides the ability to cover a broad optical regime from ˜3.4 eV (GaN) to ˜0.64 eV (InN). Similarly, tuning the Aluminum (Al) composition in the AlGaN ternary alloy allows the transition energy to change from ˜3.4 eV (GaN) to ˜6 eV (AlN).
The InGaN ternary alloy with high In content has been recognized for its importance in achieving optical emission and absorption devices covering the visible spectral regime from blue to red emission, while the AlGaN ternary alloy is critical for application in deep-UV regime. However, the experimental realization of such material systems has been limited by the challenges in growing conventional ternary and quaternary alloys with high indium and aluminum composition.
In particular, the conventional epitaxy of InGaN alloy with high In composition results in a phase separated material system, which leads to detrimental issues in the electronics and optoelectronic properties of this alloy. The limitation of growing high quality InGaN alloy with high In content has been one of the major barriers in the realization of high performance optoelectronic devices employing indium rich InGaN alloys for longer wavelength applications. Therefore, new strategies are necessary to access the epitaxy of high crystalline quality III-Nitride quaternary and ternary material systems and eventually achieve the broad tunability of optoelectronic properties in the III-Nitride platform.